The present application relates to a method for manufacturing a display device and to a display device. In particular, it relates to a method for manufacturing a display device, in which a plurality of organic electroluminescent elements are disposed, and a display device produced by this method.
An organic electroluminescent element taking advantage of electroluminescence (EL) of an organic material (so-called organic electroluminescent element) is configured by holding an organic layer, which is a laminate of a hole transporting layer, a light emitting layer, and the like, between a lower electrode and an upper electrode, and has been noted as a light emitting element capable of emitting high luminance light by low voltage direct current driving. A display device including such an organic electroluminescent element (hereafter simply referred to as a display device) is an excellent flat panel type display device and has been developed toward the scale-up of screen from the viewpoint of the color reproducibility and the response speed.
The above-described display device is allowed to deliver higher performance on the basis of active matrix drive by including thin film transistors (TFTs) to drive organic electroluminescent elements. In the active matrix-driven display device, an interlayer insulation film is disposed covering TFTs, and organic electroluminescent elements are disposed on the interlayer insulation film. Lower electrodes of individual organic electroluminescent elements are formed on the interlayer insulation film by patterning on a pixel basis while being connected to the TFTs. An organic layer of the organic electroluminescent elements is disposed on these lower electrodes. An upper electrode is disposed as a solid film common to organic electroluminescent elements of individual pixels, while organic layers are held between the lower electrodes and the upper electrode.
For the above-described active matrix-driven display device, a so-called top emission type, in which the emitted light is taken out from the side opposite to a substrate provided with the TFT, is effective at ensuring an aperture ratio. In this case, it is desired that the upper electrode is formed from a transparent material or a translucent material. However, the upper electrode including such a material as a solid film common to individual pixels has a high resistance value and display quality is significantly deteriorated due to a voltage drop. Consequently, the resistance of the upper electrode is reduced by forming an auxiliary wiring between pixels as the same layer with the lower electrode and connecting the upper electrode to the auxiliary wiring.
However, as pixel sizes and pixel pitches have been made finer in recent years, organic layers are formed having different colors on a pixel corresponding to each color of RGB basis, and tend to significantly extend in between pixels and cover the auxiliary wiring. In the configuration in which the organic layer is formed as a solid film common to individual pixels in consideration of the limit of differentiation in colors of the organic layers due to the above-described miniaturization, all over the surface of the auxiliary wiring is covered with the organic layer. In this case, the contact between the auxiliary wiring and the upper electrode becomes poor due to the organic layer on the auxiliary wiring.
Consequently, a method in which the organic layer on the auxiliary wiring has been removed by ablation through laser irradiation has been proposed. In this case, the irradiation portion of the laser light (radiant ray) is set by using a mask having an opening at the position corresponding to the auxiliary wiring, and the organic layer portion on the auxiliary wiring is selectively ablated. Alternatively, the laser light is applied after being aligned with the auxiliary wiring and, thereby, the organic layer portion on the auxiliary wiring is selectively ablated (refer to Japanese Unexamined Patent Application Publication No. 2005-11810, in particular, paragraphs [0031] and [0032]).
However, according to the above-described method disclosed by Japanese Unexamined Patent Application Publication No. 2005-11810, a misalignment between the auxiliary wiring and the mask opening and a misalignment between the auxiliary wiring and the position of the laser irradiation tend to occur, and a reduction of the yield results. In particular, in the method in which a mask is used, the production cost is increased due to the use of the mask. In the method in which the laser light is applied after being aligned with the auxiliary wiring, an operation time is increased as compared with that of the laser irradiation by one operation and, therefore, the production efficiency is reduced.
It is desired to provide a method for manufacturing a display device provided with organic electroluminescent elements and a display device produced by the method, wherein an organic layer on an auxiliary wiring is removed with high precision by one operation and, thereby, the yield is improved and the productivity is improved.